1. Field of the Invention
The present invention relates to a computer system and external storage therefor. In particular, the computer system includes devices or nodes which have peculiar device ID""s (identifiers) and are connected with one another through an interface or network, such as SCSI, IPI (Intelligent Peripheral Interface) or Ethernet, for exchanging data, commands, messages etc.
2. Related Art
As stipulated in, for example, ANSI X3. 131-1986, xe2x80x9cSmall Computer System Interface (SCSI)xe2x80x9d issued by ANSI (American National Standards Institute), the peripheral devices of a prior-art computer system have peculiar device ID""s, respectively. The LBA (Logical Block Address) lengths of the devices, the types of the devices (such as a random access device, a sequential access device, a rewritable device, and a read only device), etc. are fixed for the respective devices by standards. In addition, although not standardized, management for the data reliabilities of the individual peripheral devices, management for backing up the devices, etc. are carried out for the respective devices at the request of the OS (operating system) of a host computer.
The prior-art technique is incapable of or has difficulty coping with a case, for example, where a magnetic disk storage device having a large capacity is divided into a plurality of partitions with the intention of managing the partitions as separate storage areas having different characteristics (in points of the LBA lengths, the backup management, etc.). Accordingly, expensive and large-sized magnetic disk storage devices need to be installed for respective sorts of data of different properties, such as ordinary file data and image data.
Further, there is no consideration for sharing the peripheral devices between a plurality of hosts. The exclusive control between the hosts in the case of a shared magnetic disk storage device cannot be performed on the device side, and is inevitably entrusted to the management of the host side. For this reason, it is possible that some operations of the user of the computer system may bring about a situation where data held in the magnetic disk storage device are destroyed.
Further, in case of a network including therein a node which is physically connected in the same network, but which uses a communication protocol differing from that of the other nodes, it is difficult for such a single node to use two communication protocols properly and therefore the single node has difficulty communicating with the other nodes. Therefore, expensive and large-sized magnetic disk storage devices must be installed for the respective different communication protocols.
The first object of the present invention is to solve the problems described above, and to provide a computer system which is permitted to handle data having different properties using an identical peripheral device, and also an external storage device which serves as the peripheral device.
The second object of the present invention is to provide a computer system which is permitted to share a peripheral device among a plurality of computers.
The third object of the present invention is to provide a computer system which is permitted to share a peripheral device between computers having different communication protocols.
In order to accomplish the first object, the computer system according to the present invention is constructed so that peculiar device IDs (identifiers) are respectively allocated to a computer and the peripheral device, and that a plurality of device IDs are allocated to the peripheral device.
Also, in order to accomplish the first object, the external storage device according to the present invention is constructed so that a plurality of partitions are set therein, and that device IDs are allocated to the respective partitions.
In order to accomplish the second object, the computer system according to the present invention is constructed so that particular device IDs are respectively allocated to the plurality of computers and peripheral devices, and that a plurality of device IDs are allocated to the specified peripheral device.
In order to accomplish the third object, the computer system according to the present invention is constructed so that device IDs are allocated to the respective computers, and that device IDs differing for the respective communication protocols are allocated to the peripheral device.
In accordance with the first-mentioned construction of the present invention, when the computer has selected the peripheral device by designating any of the plurality of device IDs allocated to the peripheral device, this peripheral device responds to the computer, and the computer can access the peripheral device in regard to the designated device ID. Accordingly, the peripheral device appears to the computer to be a number of devices, in fact as many as the number of allocated device IDs, and the computer can handle the data of the different properties by the use of the peripheral device.
With the second-mentioned construction, the device IDs are respectively allocated to the partitions of the external storage device. Therefore, when the computer has selected the external storage device by designating one of the device ID""s, it can access the partition having the designated device ID. Accordingly, the partitions form separate devices when viewed from the computer, and the data with properties differing for the respective partitions can be written into and read out of these partitions.
With the third-mentioned construction, when the separate computers have selected the specified peripheral device by designating the pertinent ones of the plurality of allocated device IDs, they can access the peripheral device in regard to the designated device IDs. In this case, when the plurality of device IDs allocated to the single peripheral device are individually held in correspondence with the separate computers, the peripheral device becomes capable of performing the exclusive control between the computers. Moreover, when at least two computers are allowed to designate a predetermined one of the device IDs, they can share the peripheral device by using this predetermined device ID.
With the fourth-mentioned construction, the device IDs for the respective communication protocols are allocated to the peripheral device. Therefore, no matter which communication protocol the computer having selected the peripheral device may have, the computer can access the peripheral device in regard to the device ID designated by this computer. Accordingly, the plurality of computers having different communication protocols can share such a peripheral device.